In a hydrocracker large hydrocarbon molecules are cracked into smaller molecules in the presence of a catalyst and hydrogen. It is desirable to carry out the hydrocracking process with a maximum of efficiency. Ideally this maximum efficiency is achieved by a maximum percentage conversion at a set of otherwise constant process parameters. However, certain process parameters, such as the availability of hydrogen, sometimes cause the hydrocracking process to be carried out at a smaller percentage conversion. However, in this case, too, the maximum percentage conversion achievable under these circumstances is desirable to be achieved.
One of the problems arising when an automatic control for a hydrocracker is to be designed results from the fact that the composition of the oil fed to the hydrocracker is not constant. In addition, the temperatures of the feedstreams are not constant. Thus, it would be desirable to have available an automatic control for a hydrocracker which would keep the actual conversion at a given set point value despite variation in oil feed composition and/or feedstream temperature.